Hidden agenda here, but as a single unit to increase air defense. A line fixed to one ground square, and a line leading up to a floating balloon or kite. The purpose is to be a trap for air units, but if its on a line then its not a hidden trap.

The hidden agenda is that the line could also work as a conducting rod, maybe the balloon or kite gets burnt on one lightning hit. The trap would also be lost by being ripped out of the ground by a large air unit, like dragon or balloon. Taking a single air unit out in the tangle. Or be disabled by cutting the ground attachment with a ground troop. This way, you have a means to protect a small range from lightning attacks, but also a means to disable that protection if your troops got that far in.
You might argue that if you got troops in that far anyway, you will have obtained and earned the de anyway. So no one would mind losing their de, but it could reduce the current effectiveness of lightning hits. Lightning would be attracted to it from say 4 squares around the ground latch point, but only damage the air unit that crosses the cable path.

Hopefully there is enough of a change in the above suggestion for it to not be treated the same as every other lightning protection suggestion.